Removed unneeded line segments.
Moved declarations to constrainedly section.

This was done to propagate the parameter values to models that
redeclare these instances.
Changed source and sink models.

This was done to remove overdetermined but consistent equations for the
initialization problem.
Added missing comment.
Exposed parameter initialize_p.

This is required to be able to overwrite the default value of this
parameter.
The default value needs to be overwritten for models that stagger
multiple volumes, such as a finite volume model of a heat exchanger. In
this situation, all except the first volume need to set initialize_p =
false.
Updated reference files.
Merge pull request #78 from iea-annex60/issue61_dymola2015

Issue61 dymola2015

 -A change from protected to public for the parameter initialize_p in the energy balance. This was needed to avoid overspecified but consistent initial equations for finite difference heat exchanger models in which multiple volumes are connected in series. Otherwise, Dymola issues a long warning message.
 - A change to examples to avoid overspecified but consistent initial equations.
 - Some minor code cleanup.